Definition
A 'line' is defined as the current odds or pointspread for a given sporting event matchup. It is variable and is dependent upon the amount of money a sportsbook is receiving on such a matchup.
Line movements
As stated above, a line is not static and its movement is dependent upon where the money
is flowing. In general, a line moves in the same direction as where most of the money is going. For example, if basketball team A at -3 is being bet heavily, then this line will bump up to -3.5, or possibly even -4. A sportsbook will, at first will move the juice from -110 to -115, then move the line.
Reverse line movements
As it implies, a reverse line movement moves against where the money is flowing. In this circumstance, smart, or sharp money is driving the line towards the opposite way of where the money is flowing. For example if team A opens up at -3, and is currently bet up to -4, but the majority of the money is going towards team B, then playing team A on the spread can be considered a sharp, reverse line movement game. A great website to see where the money is flowing is www.sportsbook.com. This sportsbook gives the general public the opportunity to peek into its records and see exactly where the money is going.
Where and how is it made?
Most lines are derived from the Las Vegas Sports Consultants (LVSC). These oddsmakers work everyday analyzing stats and deriving the lines that sportsbooks around the world use. There is usually a group of people who construct a line and then a trial run. During this period, sharps and the like bet on the lines and the lines are adjusted accordingly. If a line is way off, it will be taken off the board and readjusted. Another company that derives the line is www.betcris.com. This sportsbook releases its lines the earliest, as compared to its competitors. Other sportsbooks, fearful of the sharps, first wait for the line movements at betcris, before they post their own lines.
Summary
In conclusion, the line is the odds or pointspread that is determined by oddsmakers for a given sporting event matchup. It constructed by a team of oddsmakers and is first tested by sharps before it is released to the general public. If read correctly, one may follow the smart money and beat the sportsbooks in their own game. Lastly, the line is variable and is dependent upon where the money is fl